In short, mixing stronger benefits with weaker benefits dilutes the overall argument.
For example, compare the following two statements:
This community is an exclusive place where you can learn and share best practices with the top experts in the industry.
This community is an exclusive place where you can learn and share best practices with the best experts in the industry. All members also get a free SWAG box and a $10 Amazon gift card.
This is an extreme example, but you get the idea. Even though the latter statement offers more, the former statement is more persuasive.
This applies to any message you send to persuade any members to do anything. When you mix weaker benefits with stronger benefits, it dilutes the stronger benefits.
Consider this when you promote your community, try to recruit superusers, host events, or send any communication to members. Figure out what members really need and lead with it.